A federal judge has blocked a power line under construction in Iowa and Wisconsin from crossing the Mississippi River after finding the government’s environmental review was inadequate. Judge William Conley’s ruling throws the fate of the Cardinal-Hickory Creek transmission line into question just months after utilities began construction on the $492 million project.

Conley sided with four conservation groups that sued two federal agencies over approvals of the contentious 102-mile line between Dubuque, Iowa, and Middleton. In an order, Conley said the Rural Utilities Service’s environmental review did not give adequate consideration to alternatives and therefore failed to comply with federal law.

He ruled the U.S. Fish and Wildlife Service’s decision to grant a right-of-way through the Upper Mississippi River National Wildlife and Fish Refuge was “arbitrary and capricious” and that the line is not compatible with the refuge’s mission.